Except he's completely wrong. And it has nothing to do with fandom. I haven't even watched most of the MCU myself and definitely don't associate with the fandom much.
It's fine to not like the MCU. There's nothing wrong with that. But saying it's not "cinema" is just gatekeeping nonsense in the same way that lots of stupid delineations between low art/high art are. Like, his stuff is cinema, certainly. But so is the MCU. They both are, and there's no need to put one higher or lower than the other. They're both art, both doing their own things for their own respective audiences, and that's fine: neither need to be higher or lower simply for targeting different audiences or being about different kinds of subject matter. They're both art, both cinema all the same.
Or on a completely different subject, for a different example, I follow A LOT of different artists on Twitter. These include a lot of say Japanese Pokémon and Kirby fanart. In addition to that though, I follow a number of paleoartists on Twitter who are from time to time commissioned to do scientifically-accurate artwork to the best of our current understanding to promote studies on the discovery of new species of creatures/fossils/etc. Then just within that latter category of paleoartists, including doing serious stuff like that sometimes, a lot of them also engage in speculative fiction, drawing fictional creatures just for fun.
Every single one of those subject matters are art all the same. Regardless of the subject matter, the amount of effort and passion and detail put into that stuff is exactly the same. The subject matter and "seriousness" or lack-there-of doesn't change anything, and so it's all art all the same and delineations between high art and low art and whatever just make absolutely no sense and serve no purpose to me. Especially since so many times, one of the consequences of that high art/low art/this-is-this/that-is-that nonsense is that it just makes artists so ashamed of the amount of work they put into stuff that they themselves are passionate about because it's something that society doesn't deem as high art or worth that effort and thus they feel super pressured into doing what that something is instead of what they personally are passionate about, and it just makes them miserable over stuff nobody should care about to begin with instead of being supportive to artists regardless of what they're working on, time, and time, again.
So, no, what he was saying was complete nonsense. Like, it's fine not to LIKE the MCU. Absolutely nothing wrong with that at all. Everyone has their own tastes, nothing can be for everyone, and that much is fine, of course.
But this "this is cinema, this isn't"; "this is high art, this is low art"; "this is this, this is that" garbage is just that, garbage, and I hate it in every context I see it in because without fail it's just putting other people's work down for no good reason and there's no purpose in thinking that way. Again, it's fine not to like certain art or certain forms of entertainment. Absolutely nothing wrong from that. But going that extra step from just saying "I personally don't like this" to "I don't like this, and not only do I like this, it's inherently lesser than this other form of art, I not only don't like it but think it shouldn't count or be regarded as art period" is completely unnecessary, serves absolutely no purpose, and I will never accept that line of argument or thinking from anyone, ever, because there's just no purpose in taking that extra step other than being a complete douche and putting people down over completely petty nonsense for no reason.